The invention relates to a process and an apparatus for effecting gas-liquid reactions in the presence of a dispersed catalyst. The invention particularly applies to the catalytic hydroconversion of hydrocarbons and will be described in detail with reference to a preferred embodiment.
According to a known process, heavy hydrocarbon feedstocks are hydrotreated in liquid phase with a dispersed granular catalyst, and particularly with a bed of catalyst in the expanded form, the expansion resulting from the upwards circulation of the liquid hydrocarbon charge and the hydrogen containing gas. An example of this process is known as the H-oil process. In such a process, the catalyst is not quite efficiently used; as a matter of fact, the catalyst discharged from the reactor is a mixture of strongly deactivated catalyst, partially deactivated catalyst and nearly fresh catalyst, and the sorting of the catalyst particles in relation with their deactivation degree is difficult.
According to another embodiment of this technique, a series of superposed beds of the above type may be used. Fresh catalyst is supplied from the top of the reactor and distributed throughout the stages when applying the process. The catalyst is discharged from the lowest stage. This offers the advantage of improving the rate of utilization of the catalyst before its discharge from the process. The main difficulty, in a reactor of this type, lies in the mode of transfer of the catalyst from one stage to another.
According to a first proposition, the catalyst drops continuously throughout the chambers of the apparatus. Such an apparatus cannot be operated easily: the catalyst flows down irregularly; in some cases, plugging of the transfer ducts occurs; in other cases siphoning or fluidization stoppage occur. Relatively efficient running is only obtained at a relatively high drop rate of the catalyst, so that the latter is not well utilized.
According to another proposition, valves are used to control the drop of the catalyst. Valves are not tight when used in the presence of catalyst particles; they deteriorate quickly and their setting up inside the reactor is a real problem, as concerns their control and maintenance, in view of the temperature and pressure conditions and the nature of the reaction medium. Their setting up outside of the reactor obliges to make holes in the wall, which makes it weaker to the high temperatures and pressures. Finally, opening the valves modifies the pressure distribution in the reactor and results in siphoning and even fluidization stopping in the concerned part of the reactor.